People gather for information during a Planned Parenthood Affordable Care Act outreach event for the Latino community in Los Angeles, Calif., Sept. 28, 2013. Enrollment for the Affordable Care Act, sometimes referred to as Obamacare, begins on October 1.

Washington — Most Americans already have health insurance, either through work, a family member, or a government program like Medicaid or Medicare. But that doesn’t mean they won’t have anything to do with the online marketplaces, or “exchanges,” that go live on Oct. 1.

In fact, some Americans will discover – or may already have – that their employer is opting out of providing insurance to their employees and is instead sending them to the exchanges to buy insurance. Others who already buy their coverage on the individual market may find that their old venue for purchasing insurance is no longer selling plans.

For example, AARP – the powerful interest group for older Americans – is no longer offering health insurance plans. Many AARP members are under age 65 and therefore don’t qualify yet for Medicare. So those in the 50-to-64 age bracket who are self-employed or not working, and are able to afford insurance, are buying it on the individual market.

A message on the AARP website under the tab “Major Medical Coverage” announces that the group’s “Essential Premier Health Insurance Plans, insured by Aetna,” were no longer available to new applicants as of Sept. 2, 2013.

“As a result of the many health coverage options and policies available under the ACA [Affordable Care Act], AARP will not be co-branding a 50-64 health insurance product for sale in the 2014 exchange marketplace,” the site says.

An AARP customer service representative suggests a caller visit Healthcare.gov – the Department of Health and Human Services website on the new health care law – to find out the options for new insurance. He also suggests that a current customer can buy insurance directly from Aetna. But such a plan, bought outside the new health insurance exchange, would not be eligible for a federal subsidy, regardless of one's income level. The customer can also shop for insurance on his or her state’s exchange, and possibly get a subsidy.

Either way, President Obama’s frequent assertion – that “if you like your health-care plan, you can keep your health-care plan” – is proving to be not quite true for some people, and not just AARP customers.

But on the bright side for the already-insured, there are plenty of aspects of the ACA that make a lot of people happy. Under the law, insurers can no longer reject someone with a preexisting condition, kick someone off their insurance if they become ill, or put an annual or lifetime cap on their coverage. The law also requires plans to provide a range of preventive screenings with no co-pays and allows people up to age 26 to be covered on their parents’ plan.